Material ~ The material of a wire has a great affect on how fluently the electrons can flow through it. Wires of different materials are used for different purposes, and these different materials (metals) have specific functionalities in electrical circuits. Copper is mainly used in the wiring system and electrical circuits because of its low resistance and efficiency of energy. Copper comes second to the word’s best electricity conductor, which is silver, but companies do not use it as it is very costly for national use. The opposite is an alloy called Nichrome (80% nickel and 20% Chromium), as it has a high resistance and is regularly used for heating element.
Difference of resistance in different metals depends how many free electrons the material contains. A lesser amount of energy will be needed for the flow of electrons if there are more free electrons in the wire. As we (at our level of studies) do not have the privilege to use as sophisticated equipment as advanced scientists, there is no way we can know the number of free electrons of the wires we are using. So we can understand that Nichrome must have a small amount free electrons, and copper must have more free electrons.
Length ~ The way in which the electrons flow through the wire is by detaching from their atoms, and then flowing around the circuit by being pushed around by the energy of the battery, all squashed together. The wire of the circuit itself has some resistance affecting the current, but slightly, so we cannot tell. It depends on the properties of the material being used. Any wire would do this. So if the length of the wire is doubled, the resistance is doubles also, because twice the length of wire is equivalent to two equal resistances in series. Resistance increases with the length of the wire, so we can say that resistance is proportional to length.
Thickness ~ In a thicker wire submits less resistance to current than a thinner one (of the same material) because electrons flow through the metal wire, similar to water flowing through a hosepipe. When current flows within a wire, electrons bound from atom to atom in response to the charged particles of the electric field in a circuit, so a conductor with a wider cross section allows more electrons to interrelate with the electrical field. That means that as the thickness of the wire increases, the resistance is decreased, as electrons can flow more easily and less “packed together” through the wire. It’s like getting a stampede of 10,000 elephants through a street at full speed: the wider the street, the more easily the elephants could run through it, as they would have more space to themselves; the narrower the street, the more difficult it would be for the elephants to charge through it, and they would bump into each other, slowing each other down! If the wire is too narrow, it also tends to heat up, as friction builds because of so many electrons rushing though a narrow tunnel all at the same time.
In this case, the resistance of a wire is inversely proportional to cross sectional width, because when the cross section is doubled, the resistance is halved. So the proportion is inverted. (I finally got it right!)
Temperature ~ As I learned from the “collision theory”, if heat is applied to any matter, the particles vibrate and fire up energetically, and begin to move about more as the temperature increases. The temperature of the wire also increases by the electrons rushing through it (hence a narrower wire will heat up quicker than a thick one). As the moving particles interfere with the flow the electrons when they vibrate, the electrons have to waste time on these obstacles and deflected courses instead of going further on without delay. These obstacles slow down current and cut the flow of electrons, slightly. Therefore we can say that the resistance of a wire is proportional to the temperature of it. Temperature not only affects the resistance of a wire, but is also like an indicator, as the wire heats up when the resistance is high. So when a wire heats up, there are chances of two factors affecting the resistance- thinness of the wire and the conditions of the environmental atmosphere heating the material.
There are further more factors that affect the resistance of a wire in an electrical circuit, but the consideration of these factors will not be taken into account as their insignificance is valid. Such factors are impurities in material of the wire, thermal properties and the state of illumination at the surface. We do not need to take these factors seriously because these conditions will be the same in each case and there is no way they can corrupt the results for this reason.
But in my coursework, out of all these factors, I have chosen to investigate what affect the length of the wire (of the same material) has on the resistance of it. The material will be (as normal) copper.
My Prediction
My prediction is that as the length of the wire increases, so will the resistance. I think this because this means that, inside the wire, the obstacles that the atoms create will be additional and the electrons will have to rush past these deflected courses and will be slowed down. Hence the more they are slowed down (or opposed) the greater the resistance. Therefore, I think that the length of the wire is in direct proportion to resistance. I hope my prediction is correct, but lets se what happens…
Apparatus
To prove and verify my prediction, I must carry out a practical which tests the resistance of the wires of different lengths. The following apparatus is what I utilised in my practical:
- Power Pack (electricity source)
- Wires (to link up a complete circuit)
- Crocodile clips (to connect circuit to the wire being investigated)
- Reel of Copper Wire (the wire I will investigate)
- Meter Ruler (to measure the copper wire)
- Ammeter (read the frequency of the current flowing through the circuit)
- Voltmeter (to read the frequency of the potential difference of the circuit)
Safety and Experimenting Fairly
Safety ~
Safety is an important issue as we are working with high voltage equipment. We must be aware of risks and the danger of electrocution. To evade the hazard of electrocution, we must first turn down the electricity knob on the energy supply pack to a reasonable figure so that the output voltage is quite harmless. Then, we should correctly assemble the circuit, before switching the power pack on. All other experimental safety precautions will be applied.
Fair Testing ~
In any case, and for every case, the investigational conditions must be kept unchanged. By this I mean to say that the temperature of the wire, state of illumination on the wire, power output from power pack, etc. must be the same for every different length of wire we test. So if the lights and the heating system in the room were switched on during the testing of the first wire, they both must be on for every test so that the change in the results is not massively different.
I will especially take the situations of recording results and measurement of wire very importantly, as a measurement error could lead to an irregular result. We must make sure that the electricity emerging from the power supply is exactly the same with every length of wire we test.
There should also be no mistake in investigating the correct material of wire each time, as a similar looking wire could easily be attached by mistake.
As the resistance will be calculated according to the length of wire, the length will increase by the same amount each time so that it is measured evenly. And each length will be experimented twice so that the results are verified and we are also reconfirmed that our practical was reliable.
Preliminary Experimentation
The only material I used was copper, as it is a reasonable wire. So, as an introductory experiment, I attached 10cm length of copper wire first and recorded the resistance; and then 20cm length of copper wire after that (increasing by 10cm) and noted the results.
As you can see, these are extremely close to each other and would not be very comprehensible to plot in a graph, so I then tried a larger figure: first I attached a 50cm long copper wire to the circuit and noted the results, and then attached a 100cm long copper wire after that (increasing by 50), and noted the results again.
These results were more understandable and easier to figure out by the plotted graph, and would be more logical to prove that resistance is proportional to the length of wire; so we decided to keep increasing the length of wire by 50cm. I will reach up to 3m so that a sensible amount of results can be plotted on the graph. And so I went on to do my final experiment.
Method of Investigation
It is important to record the method of how I carried out the practical as it is useful for explanation.
(To make the experimental setup easier to understand and get a better picture of, here (below) is a labelled diagram which shows the required circuit for the experiment, and also shows the components that were attached to it (voltmeter & ammeter)).
As we are all aware, we need the ammeter and voltmeter connected throughout the experiment, as voltage ÷ current = resistance. So accurate reading from these two meters is essential.
We first setup the series circuit (as shown above), not forgetting to attach a crocodile clip to each end of the gap in the circuit where the wire will be attached (where the red dots are above). The voltmeter should be connected from just before the copper wire to just after the copper wire; but the ammeter can be placed anywhere in the circuit, as long as it interfere with the voltmeter’s connection.
Then, as each different length of wire (measured by hand with a ruler) is connected to the circuit, the readings are recorded off the voltmeter and ammeter and put into a table. The results are then calculated correctly (according to the formula) to give us a satisfying table. This is the correct method to investigate what the affect of the length of a wire has on the resistance of it.
The electricity should be coming through a DC power pack so the currant can be altered easily and accurately. The voltmeter is used (for a second reason) used to make sure that the voltage coming out through the power pack is accurate and correct, because the accuracy of these power packs cannot be trusted.
To make sure the results are accurate, the setup needs to be precise and all settings need to be adjusted to suit our needs and give us the highest precision possible.
Experiment Outcomes
The results were written in a table and were exactly the way they were expected. Just to reconfirm my results, I carried out the experiment with each length twice.
The results of the practical were satisfying as they were correct according to the theory that the length of the wire is proportional to its resistance. It also was pleasing for me as my prediction was totally correct: the resistance did increase as the length of the wire did.
First Series of Outcomes ~
Second Series of Outcomes ~
Now, to finalise my results, I must work out the average of these results to plot the graph. The average results table is the mean of the two tables above (I will find the average by adding the two alike cells up and then dividing the total by two).
Average Outcome ~
This leaves us with a final table from which I must plot the graph and reveal the correlation.
Table to Plot the Graph ~
Graph of Average Results ~
The graph clearly represents the theory that the length of the wire is proportional to the resistance of it. We can tell this by the line of best fit increasing with the length of the wire.
To complete my report, all I now have to do now is analyse/conclude and evaluate my practical experiment.
Conclusion
According to the investigation aim and prediction, my experiment has been an entire success. My prediction that “resistance of the wire was proportional to the length of it” was 100% spot on and that proves the authentication of my practical.
The logical explanation for this conclusion is straightforward and is really uncomplicated. Anybody should be able to get the picture of this hypothesis and should not be confusing as the explanation is very practical.
Hypothesis ~
The straightforward explanation for the increase of resistance being proportional to the length of wire it affects is like a water system. If vast amount of water (current) is flowing through a large pipe (the circuit wire) it would be flowing quite easily. But if suddenly, a much smaller pipe (the subject wire) is joined onto it, the water would be slowed down by not having enough space (resistance) and the water would have to rush through more rapidly to keep up its earlier speed. The pipe would be resisting the water’s force, and this is what happens inside a wire, but with more complex course.
The electrons are pushed around the circuit by the battery and they use free electrons to thrust past. These electrons then face a number of deflected courses and confront atoms, which slow the electrons down (resistance). The less free electrons a material (metal) has, the better the electrons will be able to flow through them, hence, less resistance, and vice versa.
But in the end, all materials that obey Ohm’s Law (metals) have resistance, but do not affect anything much if kept under the correct conditions. So if the resistance of the wire is at a certain figure, double that length (of the wire) will double the resistance of it. This means that the electrons will have to travel more energetically and the current will be cut down, as resistance opposes the flow of electrons.
The hypothesis of this practical is very simple as explained above. The experiment obeyed and supported the theories and everything went well and as expected.
Now I am practically certain that ~ the resistance of a wire is proportional to the length of it.
This investigation confirms the following equations ~
R = V ÷ I
(resistance = potential difference ÷ current)
&
R µ L
(resistance is proportional to length)
Evaluation of Experimentation
There many ways in which this practical could have been improved. Certainly, there are many ways in which the accuracy of the results could have been improved, and whether our experiment was successful or not also depended on the accurateness of the outcomes and that is what makes it so scientific. If the practical would have lacked scientifically proved evidence, then the whole experiment would have been useless, and also a waste of precious time. Many improvements could have been made to gain more accurate and precise outcomes and to support the experiment’s scientific standing.
To enhance precision, we could have used higher-quality voltmeters and ammeters, so we could acquire readings of potential difference and current more accurately. This could be done by using a voltmeter and ammeter which would give us more accurate measurements by having more digits after the decimal point, because when one more decimal place is added, the reading becomes ten times more accurate than before.
As for accuracy, I would have repeated my experiment several times to gain better average results. If I only carried out the investigation twice with each length of wire, and have made slight errors in the first one, even if my second set of results were perfect, it would be irritating for me to use only two series of outcomes which are both different. This is because I am not sure which the truly correct one is, because the differed margin between the two is undefined. Repeating the test would be helpful as the average set of results would be more representative in proving the theory of Ohm’s Law. If more time was given to me, I would have had the chance to repeat my practical numerous amounts of times to achieve a genuine average.
The whole experiment depends on how accurate the equipment was. We cannot entitle the outcomes as scientifically totally accurate, no matter how many times we carry out the experiment. This is because I had used the equipment that was at a standard satisfactory class (with imperfections), not technologically advanced quality. If the equipment (which was used) was perfect, the line on the graph would have been 100% straight, but it was not, and that’s what proves this practical successful, but not perfect. This then leads to the improper measurement of the wire…
The subject wire was cut by hand using a ruler for measurement, and, undoubtedly, these measurements were inaccurate as the error scope was so large for the length to easily be wrongly measured: basically, it was unachievable to get a perfect measurement of wire. In addition to the incorrect measurement of wire, the technique in which it was connected and held in place was also deficient, as we used crocodile clips. These connectors are weak and also are not reliable as the clip may decrease the length of wire that actually conducts the electricity. In order to solve this setback, there should be an alternate and effective way to measure and connect the subject wire. As I am talking about the wire, its material might have also had impurities and might have caused slight imperfection and disagreement.
The temperature might have also caused the inaccuracy of actual resistance as the current passed through it, but that was not noticeable as the affect was so minute.
There are some arguments throughout the practical of the experiment not being perfect, but the conclusion of the investigation was efficient and dependable. The experiment itself provides evidence that this practical was capable for calculating the resistance of a wire, even though there are some disapproving technicalities (which were previously clarified). The basic bottom line is that, for the accomplishment of working out that “the length of wire is proportional to the resistance of it”, this practical was a brief, uncomplicated and efficient investigation. There is no doubt that the conclusion and outcomes are authentic.
If we put aside the disapproval of procedure (stated above in the evaluation), this investigation entirely supports my prediction and, most importantly, was a success!
The Resistance Of A Wire Is Proportional To The Length Of It
Extended Investigations
Any extended investigations could be like experimenting how the temperature, thickness and material affect the resistance of a wire. These few experiments could have been done with the same setup and would not need additional equipment.
